Screen components in projection TVs need to be reduced in thickness, to reduce total screen costs and create a thinner form factor, i.e., reduce bulk. Current configurations provide air gaps in-between screen components that can accumulate dirt or dust, materials that degrade image quality. The air gap also increases the cost of manufacturing, and the thickness of the system.
The traditional air gap used for Fresnel lenses used in projection TVs does not allow for lamination or combination of the Fresnel lens and other components in the screen. For example, Shikama has described a hybrid reflection-refraction Fresnel lens/screen in SID Proceedings 2002, p. 1252. While offering an improvement by lowering the F/# achievable with a Fresnel lens, this screen is described as using an air gap. Traditional Fresnel lenses are described in Projection Displays, Stupp and Brennesholtz, (Wiley and Sons 1999) wherein air gaps are shown.
The lenticular lens also uses an air gap to achieve the desired refraction and increased screen contrast. Improvements in lenticular lens technology include using aspheric lens shapes to improve the screen contrast by increasing the area of the black stripe region while maintaining throughput. However, this technology is also described as using an air gap, increasing the complexity of manufacturing, and the overall screen thickness.
Screen contrast needs to be improved in order for displays to perform well in bright ambient light environments. Lamp life is an important issue with projection displays, and one method for increasing lamp life is to increase system throughput. The relative positions of the light source, lenses and contrast enhancement elements of a projection screen can have an effect on screen throughput. For example, the Fresnel lens has a fixed focal length, and any variation from this in design or production of the Fresnel lens, position of the projection lens, position of the light source, position of the folding or aspheric mirrors in the system can cause a significant amount of light to be absorbed by the contrast enhancing element.
In other words, in many rear projection display systems, the light from a projection lens that passes through the Fresnel lens and lenticular lens does not form bright lines of light with constant line thicknesses, constant pitch, or parallel lines light on the black stripe region. If light is not perfectly collimated and parallel to the optic axis, then the black stripe regions may absorb more of the system intensity than is desired, thus reducing screen throughput. With most system designs, the exact angle and degree of collimation of the light incident on the screen can vary, and designing each screen component to account for these variations individually can be cost prohibitive. To counteract for these issues, systems and screen components are either designed with very high tolerances or suffer reduced brightness or contrast.
Fresnel reflections can also reduce the system throughput and can result in ghost images in certain situations. The ability to reduce these reflections is limited because low-cost anti-reflection coating techniques typically require planarized surfaces.
Complete screens for high resolution, high contrast projection displays are manufactured using non-continuous assembly techniques. In order to reduce the cost of manufacturing, techniques for producing a screen would need a complete roll-to-roll manufacturing method.